Membrane tank for liquefied gases

ABSTRACT

The dimensions of the membrane tank are so selected that when it is cooled by liquefied gas charged therein and contracted, the flat portions may just contact with the inner surfaces of an insulating material lined over the inner wall of a shell structure. Restraining forces are applied to the membrane tank when the latter is installed into the insulating material structure. When the liquefied gas is charged into the membrane tank, the bending stresses generated are almost zero and the tank is subjected only to the hoop tensions.

United States Patent [191 Kuniyasu et al.

MEMBRANE TANK FOR LIQUEFIED GASES Inventors: Tsuneo Kuniyasu, Fujisawa;Daizo Goto; Takayoshi Miyanari, both of Tokyo, all of JapanIshikawajima-Harima Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed: Sept.20, 1973 Appl. No.: 398,926

Assignee:

Foreign Application Priority Data 22, 1972 Japan 47-95403 30, 1973 Japan48-12170 US. Cl. 220/9 LG; 62/45 Int. Cl B65d 25/18 Field of Search62/45; 220/9 LG; 114/74 A References Cited UNITED STATES PATENTS 10/1971Yamamoto 220/9 LG 51 Sept. 9, 1975 Yamamoto et a1 Yamamoto et al PrimaryExaminer-Meyer Perlin Assistant ExaminerRonald C. Capossela Attorney,Agent, or Firm-Scrivener Parker Scrivener & Clarke [5 7] ABSTRACT 3Claims, 8 Drawing Figures PATENTED SEP' 91975 SHEET E. OF 3 PATENTED SEP91975 SHEET 3 0g 3 MEMBRANE TANK FOR LIQUEFIED GASES The presentinvention relates to a membrane tank for liquefied gases.

The conventional liquefied gas storage tanks are generally divided intoa self-supporting type and a membrane type. In case of theself-supporting storage tanks, the tank shell is so designed andfabricated as to withstand the hydraulic pressure as well as gaspressure of liquefied gas stored in the tank. As a result, the tankshell is complex in structure, and requires a large amount of veryexpensive material, and welding. Furthermore the liquefied gas storagetanks using materials difficult for welding will be very expensive. Inthe case of the membrane storage tanks, the hydraulic pressure as wellas gas pressure are supported by a shell structure lined with insulatingmaterial, so the construction can be very thin and simple. Furthermore,the fabrication cost is inexpensive because the amount of expensivematerial and welding can be reduced. However the membrane tankfabrication method is extremely difficult because complicated creasesmust be provided in order to absorb the contraction of the membrane tankdue to the contact with low temperature liquefied gas. Furthermore thedamages of the membrane tank tend to start from the creased portions.

To overcome these problems, there has been proposed the so-called flatmembrane tank type in which the deformation or contraction of themembrane tank is absorbed by the deformations of the cylindrical ridgeportions thereof, but there is a disadvantage in that local bendingstresses are produced because the deformations are concentrated at thecylindrical ridge portions.

In view of the above, the primary object of the present invention is toprovide a liquefied gas membrane storage tank which generates only hooptension but almost no bending stress when the membrane tank is cooled toa temperature of liquefied gas stored therein, so that the stressgenerated can be prominently re duced and can be uniformly distributed.

The objects, features and advantages of the present invention willbecome more apparent from the following discription of preferredembodiments, in conjunction with the accompanying drawing.

FIG. 1 is a cross sectional view of a conventional flat membrane tankfor liquefied gas;

FIG. 2 is a fragmentary view thereof, in enlarged scale, used for theexplanation of the stress distribution at the corner thereof;

FIG. 3 is a cross sectional view of a first embodiment of the presentinvention;

FIG. 4 is a view used for the explanation of the deformation thereof;

FIG. 5 is a view illustrating the stress distribution thereof;

FIG. 6 is a perspective view ofa second embodiment v the presentinvention. Referring to FIG. 1, a flat membrane 1 is placed on the innerwall of a shell 3, having in between an insulating material 2. Theridges of the membrane are cylindrical and vertices of the membrane arespherical. When low temperature liquid is charged, the flat membrane 1is contracted as shown by the lines 1 and then pressed against theinsulating material 2 under the hydraulic and gas pressures of the liquid as shown by the chain lines 1". The deformation of the membrane tankdue to the low temperature and pressure of the liquid is absorbed by thedeformations of the ridges. Since the flat membrane tank of the typedescribed is very simple in construction, it is advantageous from thestandpoint of material and manufacture, but it has a disadvantage thatlocal bending stresses are generated as shown and a and a in FIG. 2because the deformation of the membrane tank mainly occurs at itsridges.

Referring to FIGS. 3 5, the first embodiment of the present inventionwill be described.

The insulating material 2 which also serves to transmit the innerpressure of the membrane tank T to the shell 3 is lined over the innerwalls of the shell 3. The outer dimensions of the membrane tank T are sodetermined that at room temperature they are larger than the innerdimensions of the insulating material 2 as indicated by the broken lineslb in FIG. 4 but when the membrane tank T is cooled to a temperatureequal to that of the low temperature liquid charged into the tank themembrane tank T is so contracted that the flat portions thereof contactwith the inner surfaces of the insulating material 2. The ridges of themembrane tank T are cylindrical. When the membrane tank T is installed,the restraining forces are applied to the tangent lines, that is theboundary lines A and B in FIG. 4 between the flat faces and the ridgesso that the ridges are deformed as indicated by the chain lines la inFIG. 4 while the flat portions are pressed against the inner surfaces Cin FIG. 4 of the insulating material 2.

Since the insulating material 2 is lined over the inner walls of thetank shell 3, there is a sufficient space 4 at every comer into whichthe deformed ridge portion of the membrane tank 3 extends as indicatedby the chain lines 1a. Even after the restraining forces are relieved,the flat portions are pressed against the inner surface of theinsulating material 2 sothat the deformed ridge portion may remain inthe space 4 at room temperature and the bending stresses are generated.

When the membrane tank T is cooled by the low temperature liquid, it iscontracted so that the deformed ridge portion is gradually retractedinwardly. At the temperature of the low temperature liquid the flatportions just contact with the inner surfaces of the insulating material2 and the ridge portion is curved with a predetermined radius asindicated by the solid line in FIG. 4. Therefore no bending stress isgenerated, so that the membrane tank T is subjected only to the hooptension H. However because of the expansion of the membrane tank T dueto the hydraulic pressure or inner pressure I of the low-temperatureliquid, very small bending stresses are generated, but they arenegligible in practice. In order to eliminate completely the bendingstresses, the radius of curvature of the membrane is further decreased.

Next referring to FIGS. 6 8, the second embodiment of the presentinvention will be described. According to the second embodiment of thepresent invention oppose to the first embodiment, no restraining forceis applied to the vertex portion to deform the latter when the membranetank is installed within the shell.

The convex cylindrical ridge portion Y where the adjacent flat surfacesX meet has a radius R and the convex spherical vertex portion has aradius R smaller than R The adjacent flat portion X, the cylindricalridge portions Y and the spherical vertex portion 0 are connected toeach other through a triangular connecting portion P. The outerdimensions 5 of the flat surface X at room temperature are greater thanthe radius of the spherical vertex portion 0 by 5. The value of 6 isdetermined depending upon the dimensions and material of the membranetank T. For example when the membrane tank T is contracted by 1., at atemperature of liquid stored therein, 8 is so selected as to be equal to5, in' order to substantially eliminate the bending stress at thecylindrical edge Y. The distance 1 between the vertex 7 of theconnecting portion P on the side of the spherical vertex portion 0 andthe vertex 8 on the side of the flat portion X is taken as 1 z /2 R tofacilitate the fabrication, and the connecting portion P has a surfacesubstantially similar to a conical surface so that it may be easilydeveloped and do not cause undue stress.

When the restraining force is applied to the membrane tank T so as todecrease its outer dimensions 5 to the dimensions indicated as thebroken lines 6 in FIG. 8 to install the membrane tank within the shell,the outer dimensions of the membrane tank can be easily deformed eventhough the force is not directly applied to the spherical vertex portion0. When the forces are applied to the membrane tank T, the cylindricalridge portions Y is deformed, but no force is transmitted to thespherical vertex portion 0 because the deformation is absorbed by theconnecting portions P. In other words no force is needed to be appliedto the spherical vertex portion when the membrane tank T is installedwithin the shell or the insulating material. In the membrane tank Tinstalled within the shell, no high bending stress is generated even atroom temperature. When it is cooled to a temperature of a lowtemperatureliquid stored, it is contracted so that substantially no bending stressis generated and the membrane tank is subjected only to the hooptension.

The insulating material is so lined on the inner surfaces of the shellso as to provide a space at every corner so that the membrane tank ofthe second embodiment may be installed in a manner describedsubstantially similar to that described in the first embodiment. Thatis, the ridge portions of the membrane tank may be freely deformedwithin these spaces. The effect of the second embodiment installed aresimilar to that of the first embodiment.

It is understood that in addition to the preferred embodiments describedabove various modifications may be effected without departing from thetrue spirit of the present invention.

The advantages of the membrane tank in accordance with the presentinvention may be summarized as follows:

i. In the membrane tank installed almost no bending stress is produced,and the membrane tank is subjected only to the hoop tension. Thethickness of the wall of the membrane tank can be therefore reducedconsiderably, and the damage to the membrane tank can be avoided. Themembrane tank has sufficient strength and can be fabricated in a simplemanner at a low cost.

ii. Since the spaces are provided at every corners of the insulatingmaterial lined on the inner walls of the shell, the externally entendeddeformations of the cylindrical ridge portions of the membrane tank canbe allowed when the membrane tank is to be installed within the shell.Furthermore the radius of the cylindrical ridge portions may be reduced.

iii. The spaces may be used for the piping system associated with themembrane tank and access for the maintenance and inspection.

iv. According to the second embodiment, the thermal constraction of themembrane tank can be absorbed by the connecting portions with a conicalsurface, so that the forces are applied only to the cylindrical ridgeportions and not to the spherical vertex portions of the membrane tankwhen the latter must be reduced in size so as to be installed within theshell. Furthermore even when the restraining force is applied, therearises no problem on the strength of the membrane tank, and the lessrestraining force will be required. The membrane tank can be fabricatedat low cost because the spherical vertex portions may be fabricated in asimple manner.

v. The contraction of the cylindrical ridge portions can be relieved inthe spaces at the corners of the insulating material, and theinstallation of the membrane tank within the insulating material may bemuch facilitated.

What is claimed is:

1. A storage container for liquefied gas comprising an outer shell, aninner lining of insulating material engaging the inner walls of saidshell, and a flexible membrane tank within said inner lining, said tankincluding flat side, top and bottom portions and flat end portions, theside and top and bottom portions being connected by arcuate ridgeportions each having a convex cylindrical surface, the dimensions ofeach flat portion of the tank being larger at room temperature than thecorresponding portions of the lining, said dimensions being such thatwhen the membrane tank is assembled within the lining, the flat portionsof the tank engage the corresponding flat portions of the lining, withthe arcuate ridge portions received within corners formed betweenadjacent side portions of the lining, said arcuate ridge portionsretracting inwardly when the tank is cooled by liquefied gas placedtherein.

2. A tank as set forth in claim 1 wherein a space is provided betweenthe lining and each ridge portion, the radius of curvature of the ridgeportions being decreased when the tank is installed within the lining.

3. A tank as set forth in claim 1 wherein said tank is provided withconvex sperical vertex portions when radius of curvature is less thanthe ridge portions, and the adjacent flat portions and sperical vertexportions are connected through a cylindrical connecting portion having asurface similar to a conical surface.

1. A storage container for liquefied gas comprising an outer shell, aninner lining of insulating material engaging the inner walls of saidshell, and a flexible membrane tank within said inner lining, said tankincluding flat side, top and bottom portions and flat end portions, theside and top and bottom portions being connected by arcuate ridgeportions each having a convex cylindrical surface, the dimensions ofeach flat portion of the tank being larger at room temperature than thecorresponding portions of the lining, said dimensions being such thatwhen the membrane tank is assembled within the lining, the flat portionsof the tank engage the corresponding flat portions of the lining, withthe arcuate ridge portions received within corners formed betweenadjacent side portions of the lining, said arcuate ridge portionsretracting inwardly when the tank is cooled by liquefied gas placedtherein.
 2. A tank as set forth in claim 1 wherein a space is providedbetween the lining and each ridge portion, the radius of curvature ofthe ridge portions being decreased when the tank is installed within thelining.
 3. A tank as set forth in claim 1 wherein said tank is providedwith convex sperical vertex portions when radius of curvature is lessthan the ridge portions, and the adjacent flat portions and spericalvertex portions are connected through a cylindrical connecting portionhaving a surface similar to a conical surface.